As costs of energy increase along with concerns about global warming due to consumption of fossil fuels to generate energy, there is an every increasing need for more efficient lighting technologies. These demands, coupled with rapid improvements in semiconductors and related manufacturing technologies, are driving a trend in the lighting industry toward the use of light emitting diodes (LEDs) or other solid state light sources to produce light for general lighting applications, as replacements for incandescent lighting and eventually as replacements for other older less efficient light sources.
To provide efficient mixing of the light from a number of sources and a pleasing uniform light output, Advanced Optical Technologies, LLC (AOT) of Herndon, Va. has developed a variety of light fixture configurations that utilize a diffusely reflective optical integrating cavity to process and combine the light from a number of solid state sources. By way of example, a variety of structures for AOT's lighting systems using optical integrating cavities are described in US Patent Application Publications 2007/0138978, 2007/0051883 and 2007/0045524, the disclosures of which are incorporated herein entirely by reference.
Although these integrating cavity-based lighting systems/fixtures provide excellent quality light in an efficient manner and address a variety of concerns regarding other solid state lighting equipment, there is still room for improvement. For example, efficiency of the optical integrating cavity decreases if the diffuse reflectivity of its interior surface(s) is compromised, for example due to contamination from dirt or debris entering the cavity. Also, since the cavity is filled with air (low index of refraction), some light may be trapped in the LED packages by internal reflection at the package surface because the material used to encapsulate the LED chip may have a higher index of refraction. Efficiency may also be somewhat reduced if the mask or portion of the cavity around the aperture needs to have a relatively large size (producing a small optical aperture) to sufficiently reduce or prevent direct emissions from the solid state light source(s) through the cavity and optical aperture.
US Patent Application Publications 2008/0094835 to Marra et al. describes a light engine having a chamber with an aperture and a number of LED elements positioned inside the chamber. Inner surfaces of the chamber are highly-reflective and essentially non-absorbing towards light within a desired wavelength region. The reflective inner surfaces are formed by a diffuse-reflective material sandwiched between a substrate/wall and a transparent covering plate. To improve efficiency of light extraction from the LEDs, the fixture may include out-coupling elements that are optically coupled between the LEDs and the transparent covering plate. Although the cavity may be empty, this publication also suggests that the cavity may be filled with a material which has a refractive index that approaches or, preferably, matches the refractive index of one or more of the other elements of the light engine, e.g. that of the transparent covering plate. As disclosed, this filler material may be an organic medium such as a transparent liquid, particularly an oil, or a solid resin, particularly a silicone resin, possessing the desired (matching) refractive index, and which is preferably substantially non-absorbing with respect to visible light and/or with respect to the light generated inside and emitted from the LED dies.
U.S. Pat. No. 7,040,774 to Beeson et al discloses an illumination system having one or more LEDs and a wavelength conversion layer within a light-recycling envelope. In some examples, the wavelength conversion layer may fill a substantial portion of the volume of the light-recycling envelope. The light from the LED source(s) is transmitted through the wavelength conversion layer in order to convert a portion of the light of a first wavelength range into light of a second wavelength range. Light of both the first and second wavelength ranges exit the light-recycling envelope through an aperture.
These developments not withstanding, in this age of ever increasing concern over energy consumption, there is always a need for techniques to still further improve efficiency of solid state lighting fixtures or systems. Also, any modification of the structure or design of the solid state light fixture must address ancillary issues, such as circuit mounting and/or heat dissipation. For example, LED type solid state emitters generate heat, and it is important to provide effective heat dissipation to avoid damage to the LEDs or associated circuitry.